3,3'-diaminobenzidine tetrahydrochloride commonly referred to as DAB, is a chromogen that produces a brown to black end product that is insoluble in alcohol and solvents, such as xylene. This is a permanent chromogen that will not be removed when dehydrating and clearing slides at the end of the staining. One can use solvent-based or synthetic resins for coverslipping to produce a permanent cover.
3-amino-9-ethylcarbazole, known as AEC, is a chromogen that forms a rose-red end product that is soluble in organic solvents. Specimens that were IHC stained with the use of AEC must NOT be immersed in alcohol or solvents. Aqueous counterstains and aqueous coverslipping media should be used to maintain the color. AEC is also sensitive to light and can fade if exposed to excessive light.
